The generation of a streaming potential induced by changes in the zeta-potential has been used to build a general affinity sensor which measures protein interactions (Koch et al. Biosensors & Bioelectronics 1999 14:413-421). The capture agents in this set-up are immobilized on the inside of a capillary in connection with two ISFET sensors on each side of the capillary. The zeta-potential induced streaming potential difference between the two ISFETS is measured. Also see Wallin et al. Cancer Lett. 1984 March; 22(2):163-70 and Glad et al. Biosensors 1986; 2(2): 89-100.